U.S. Pat. No. 7,699,172 (McTavish et al.) entitled “Stacking Delivery Tray” discloses a stacking delivery tray that has two operative positions to accommodate different sizes of product. When these delivery trays are stacked, in order to add or remove an overlying tray, it must slide along the underlying tray. In a first or lower operative position, the overlying tray slides along a top shelf. In a second or higher operative position, the overlying tray slides along a top rail which is raised above the top shelf. In order to accommodate the two operative positions, the McTavish et al. stacking delivery tray has a top rail with breaks in it and a top shelf with breaks in it. These breaks are referred to by McTavish et. al as valleys. In view of this, it is difficult, if not impossible, to get a smooth linear sliding action along either the top rail or the top shelf. What is required is a modified sliding engagement which will facilitate a smoother more linear sliding relationship between the underlying tray and the overlying tray.